In certain types of image processing systems, especially color correction systems employed in post-production equipment, system operators observe an image on a video monitor, adjust color and other parameters of the image until it is aesthetically satisfactory, store the parameters in system memory, and apply the parameter corrections to a sequence of images forming a scene. Various types of image processing are often employed to create, enhance, compress, filter, or otherwise modify characteristics of an image. In a video signal color correction system, color corrections of motion picture film and/or video tape are typically made on a scene-by-scene basis. A “scene” is a sequential collection of images shot from the same camera, having the same viewpoint, composed in a certain way, etc. A system operator or “colorist” views a selected exemplary image or frame from a scene. The colorist then applies color corrections via a control panel to adjust video parameters such as hue, saturation, luminance, etc. of a frame image being viewed. The correction settings are stored in system memory.
After the colorist is satisfied with the adjustments he or she has made to the selected frame, the correction system, which is typically computer-controlled, applies the stored color corrections to each frame in the scene one at a time. The color-corrected frames of the scene are then recorded on film or videotape. The steps are repeated for other scenes in the film or video tape, often with different correction settings stored for different scenes. This process creates a color-corrected master film or video tape that reflects color adjustments to all frames in all scenes.
Devices are known in the art for defining a region of an image for applying one set of color corrections, with other regions of the image receiving another, separate set of color corrections. Such devices are useful when it is desired to isolate a certain area of an image to receive special image processing. For example, in color correcting a soft drink commercial it may be desirable to isolate the beverage can from the remainder of the image so as to make the colors of the beverage can stand out from the rest of the image.
Certain prior art image processing computer software, e.g. ADOBE PHOTOSHOP™, manufactured by Adobe Systems Corporation, Mountain View, Calif., employs edge detection algorithms for detecting color regions and creating paths or Bezier curves between points. Such edge detection algorithms rely upon color differences between regions to define the paths and produce odd results if there are discontinuities in the edges of a region, or if the colors defining the regions are not sufficiently dissimilar. The PHOTOSHOP™ software, for example, vectorizes an entire color region and provides no control over the number of points in the region. There is no way to modify a defined region except by changing region qualification parameters. For these and other reasons, such software is not suitable for real time applications such as a scene by scene color corrector.
A system for creating user definable windows for applying image processing is described in U.S. patent application Ser. No. 08/912,662, filed Aug. 8, 1997 entitled “User Definable Windows for Selecting Image Processing Regions.” This application is owned by the same assignee as the present invention. In this system, the luminance values of a key image are captured in a key frame buffer. The key image is edited in a “paint” mode to enhance the luminance values or eliminate regions of the image, to define a region of interest. The key image is then converted to a 1-bit image. The 1-bit image is vectorized to derive a user defined window. The user defined window, comprising a closed polygon, is converted on a frame-by-frame basis to a matte that is keyed with image processing such as color correction values. User defined windows can be edited and stored and recalled for use in other frames. A user defined window for a first frame of a scene can be transformed or morphed into a user defined window for a final frame of a scene, with the system automatically interpolating between the beginning window and the ending window so that the window is automatically moved, resized, and changed in geometry during the succession of frames in a scene.
Although this system provides remarkable improvements in isolating regions for receiving color correction in a scene-by-scene color corrector, only the luminance of the target image is employed to isolate a region of interest. Moreover, the system as described in this patent is not capable of automatically tracking a region of interest based on its color parameters (hue, saturation, and/or luminance) over a number of frames-the system therein described “morphs” the polygon from a first frame to a final frame of a scene.
There is a need, however, for a system that isolates a region of interest by its color parameters, e.g. hue, saturation, and/or luminance, or red/green/blue values, and employs those color parameters to establish and track the region of interest over number of frames in a scene, to effect automatic tracking of the region of interest over a plurality of frames.